Lecture on Senses

Introduction

• General vs. Special Senses
  • General Senses: Temperature, pain, touch, stretch, pressure
  • Special Senses: Gustation, olfaction, vision, equilibrium, audition
• Stimulus vs. Sensation:
  • Stimulus: Information detected by receptors; enters through the peripheral nervous system
  • Sensation: Conscious awareness of the stimulus, processed in the cerebral cortex

Receptors

• Range in complexity:
  • From single-celled dendritic endings to complex sense organs (e.g., eye, ear)
• Role: Monitor internal and external conditions; conduct information to the CNS
• Receptive Fields:
  • Small Field: High precision in localization
  • Large Field: General localization

Types of Receptors

• Tonic Receptors: Maintain balance (e.g., keeping head upright)
• Phasic Receptors: Signal changes (e.g., pressure on skin)
  • Acclimation: Reduced sensitivity to continuous stimuli
• Locations:
  • Special Sense Receptors: Complex organs in the head
  • General Sense Receptors: Distributed throughout skin and organs

Classification of Receptors

• Exteroreceptors: Skin and mucous membranes
• Interoceptors: Inside viscera
• Proprioceptors: Skeletal muscles, tendons, joint capsules

Sensory Modalities

• Chemoreceptors: Respond to molecules in fluid
• Thermoreceptors: Temperature changes
• Nociceptors: Detect damaged tissue
• Mechanoreceptors:
  • Touch: Light touch
  • Pressure: Vibration and stretch
• Proprioception: Changes in muscle or joint position

Gustation (Taste)

• Taste Buds: Located on dorsal surface of the tongue
• Papillae Types:
  • Filiform: Anterior 2/3, no taste buds
  • Fungiform: Tip and sides, few taste buds
  • Vallate: Posterior, many taste buds
  • Foliate: Posterior-lateral, few in childhood
• Five Basic Tastes:
  • Salty, Sweet, Sour, Bitter, Umami

Olfaction (Smell)

• Olfactory Receptors: Detect odors
  • Bipolar neurons that synapse with olfactory bulbs
• Supporting Cells: Protect olfactory nerves
• Basal Cells: Replace olfactory epithelium
• Human vs. Dog: Humans recognize fewer odors

Vision

• Photoreceptors: Detect light, color, movement
• Accessory Structures:
  • Conjunctiva: Covers cornea and sclera
  • Eyebrows, Eyelashes, Eyelids: Protect from foreign objects
  • Lacrimal Glands: Keep eyes moist
  • Extraocular Muscles: Move the eye
• Eye Structures:
  • Cornea and Sclera: Protect and refract light
  • Choroid: Vascular layer
  • Retina: Contains photoreceptors
• Optic Disc (Blind Spot): No photoreceptors
• Macula Lutea and Fovea Centralis: Area of sharpest vision

Hearing and Equilibrium

• External Ear: Funnels sound
• Middle Ear: Contains auditory ossicles
• Inner Ear: Fluid-filled chambers, includes cochlea and semicircular canals
• Functions:
  • Hearing (Audition): Sound waves to mechanical movement
  • Equilibrium: Maintains balance through fluid movement

These notes cover the main points discussed in the lecture on the general and special senses, focusing primarily on the functions, classifications, and specifics of receptors involved in various sensory modalities.